ECHINOIDEA 293 



beneath the end tooth. Peristome naked, excepting the 

 buccal plates. Test usually reddish and white spotted 



Genocidaris maculata A. Ag. 

 ■ Some smaller plates on the periproct besides the large anal 

 plate ; peristome outside the buccal plates covered by large 

 plates. Test and spines white ..... 2 



2. Test ornamented with numerous rather large, irregular grooves. 

 Globiferous pedicellariae with a single, impaired tooth beneath 

 the end tooth. Spicules C -shaped 



Trigonocidaris albida A. Agass. 



Test smooth, at most a fine reticulation in the larger specimens. 



Globiferous pedicellarise with 2-4 lateral teeth on either side, 



beneath the end tooth. Spicules irregular 3 -radiate. The 



female with the apical area raised into a prominent knob 



Hypsiechinus coronatus Mrtsn. 



All three forms are very small, scarcely exceeding 10-15 mm. 

 ill horizontal diameter. HypsiecJiinus protects its brood, the 

 young ones being found attached round the apical knob, covered 

 by the spines. The development of the two other species is un- 

 known, but Genocidaris maculata may be expected to have a 

 typical pelagic larva. 



I. Family Echinid.^ 



Test without depressions or pits ; tubercles smooth. Am- 

 bulacral plates with three or more pore pairs (oUgoporous or 

 polyporous). GiU-cuts not deep, more or less obsolete. Globi- 

 ferous pedicellarise with one or more teeth on both sides of the 

 valves, beneath the end tooth, and with head attached directly 

 to the end of the stalk, mthout a neck ; no mucous glands on 

 the stalk. Spicules simply C-shaped (Fig. 144, 4). 



Three genera represented in the British (and European) seas. 



Key to the genera of Echinidce represented in the British seas. 



1. Ambulacral plates with 3 pairs of pores (" oligoporous ") . 2 



,, ,, ,, 5-6 ,, ,, ("polyporous") 



3. Paracentrotus Mrtsn. 



2. Buccal membrane usually closely packed with tliick plates ; 



globiferous pedicellariae with outer part of valves (the blade) 

 quite open, without cross beams, and with several teeth along 

 each side (Fig. 144, 1) . . 1. Psammechinus L. Agass. 



Buccal membrane with few, thin plates ; globiferous pedi- 

 cellarise with blade more or less tube-shaped, the edges connected 

 by cross beams ; one or a few teeth along each side of the 

 blade (Fig. 144, 2) . . . . 2. Echinus Linn. 



